1. Field of the Invention
The present invention relates to an image processing apparatus which can reproduce images with different magnifications.
2. Description of the Prior Art
In order to copy at a given magnification using a conventional image processing apparatus such as a copying machine or copy unit, a desired magnification is inputted with ten keys or a special key for setting a copy magnification is used. In order to display the copy magnification preset in this manner, a display for displaying the copy magnification must be used.
In a conventional image processing apparatus of this type, a special key for setting the copy magnification or a display is used, so that the total number of keys or displays used is increased. The number of input/output operations to be performed then becomes large, the operation complex, and the operability poor.
A unit which allows stepless setting of a magnification is known. A variable resistor can be conveniently used for this purpose since it is easy to handle and inexpensive. However, unlike other input means, such as a key switch, a preset value is altered when a human hand brushes the unit irrespective of the read of inhibition mode, thus resulting in inconvenience.
In addition, when the magnification is sequentially changed in stepless fashion, the magnification which is being thus set must be displayed to an operator. When a display means for this purpose is incorporated, cost of the overall apparatus becomes high.
When a size change (magnification change) is performed with a conventional image processing apparatus, the margin at the leading edge of a copy is inadvertently changed, thus degrading the copy quality
A means for stepless change of magnification using a zoom lens has also been proposed. In a conventional means of this type, the control means is complex, and the positioning precision is low.
A copy unit has been proposed wherein a density of an original image is detected, and an exposure or a developing bias is controlled in accordance with the detected density, so that a copy image of an optimal density is obtained. In order to detect the original density, an extra original scanning step other than a normal copy operation must be performed. For this reason, a change from a manual density control mode to an automatic density control mode cannot be made during the copy operation. When the preset density becomes improper during copy operation of a plurality of copies in the manual density control mode, the copy operation must be stopped to change the mode to the automatic density control mode or the density must be manually adjusted while the first few defective copies are discarded.
Since the function to be controlled in an apparatus wherein a density is automatically changed is a heat source such as an exposure lamp or a fixing heater or is a high voltage source, if a normal control operation cannot be performed due to mechanical trouble, the problem of safety arises. Conventionally, when trouble occurs, the operator determines the cause and takes countermeasures. For this reason, an extra load is applied to the exposure lamp or the like, and the lamp life is shortened. A secondary effect on IC parts or the like cannot be avoided.
A photosensitive body used in an image formation apparatus changes its characteristics upon irradiation with light over a long period of time. These changes have a great effect on image quality and determine the life of the photosensitive body. In order to compensate for such changes in the characteristics of the photosensitive body, a method has been proposed for detecting the sensitivity of the photosensitive body and to control the light quantity or the high voltage applied to it. This method requires a complex arrangement and results in an expensive device.
In a conventional image formation apparatus of this type such as a copy unit, when phase lock loop control of a DC motor as a drive source is performed, a phase difference of the phase control cannot be easily determined, and control requires a considerable period of time.
In such a conventional apparatus, the copy operation is controlled by a motor for driving a photosensitive drum or by a drum clock generator mounted on a movable portion driven by the motor. An abnormality is detected only when no drum clock is detected. When such an abnormality is detected, the copy operation is stopped, and the abnormality is displayed. However, satisfactory control cannot be performed when two or more motors are used.
A driver is generally used to drive a scanner motor. However, when an erratic operation due to noise or an abnormality is caused for unexplained reason, the motor cannot be protected from a surge voltage.
When the copy unit must be stopped immediately for whatever reason, for example, when jamming occurs in this type of apparatus, the motor is stopped when jamming is detected. After the jamming is cleared, the optical system is returned to the home position and the next copy operation is started. Thus, the procedure for resuming the copy operation is time-consuming. In a copy unit of the type wherein an original table is moved relative to the optical system, due to the original table not being stopped at the home position, other operations may be interfered with. Especially when a DC motor is used to move the original table, the table cannot be easily moved manually, thus requiring complex preparation for resuming operations.